In clinical laboratory practice, various techniques, such as electrophoresis, are used to apply samples to substrates for separation and analysis. Electrophoresis in general is the voltage-driven migration of suspended and/or colloidal particles in a liquid or a gel, due to the effect of a potential difference across immersed electrodes. In many devices that use electrophoresis, the strategy is to apply a sample just to the surface of a substrate, then apply a voltage to separate the components of the sample. This strategy is used in techniques like immunofixation-based electrophoresis and two-dimensional electrophoresis.
Electrophoresis is often used in the study of proteins and colloidal particles from biological samples, such as evaluation of lipoparticles and lipoproteins. In immunofixation methods, such as described in U.S. Patent Application Publication No. 2012/0052594, which is hereby incorporated herein by reference in its entirety, a biological sample (e.g., serum) is applied to a substrate and the components are electrophoresed. Anti-sera containing labeled antibodies that target specific components of the blood is applied to the substrate. The antibodies attach to their antigen targets, and the targets can be identified through some means of detecting the label.
In clinical applications, it is desirable to analyze many samples in parallel on the same substrate. This reduces the cost per sample analyzed and saves substantial time. High throughput instruments and devices, such as the SPIFE 3000 Assay instrument by Helena Laboratories, are made for this purpose.
High throughput instruments use an applicator comb to apply a series of samples in a single line on the substrate. Such an applicator comb, having a design using squared-off teeth, is described in U.S. Pat. No. 6,544,395, which is hereby incorporated by reference herein in its entirety.
There is a desire in the art to increase the number of samples per substrate to increase throughput and make the method more efficient. Increasing the number of teeth per applicator comb would accomplish this goal. However, increasing the number of teeth without a change in design is not effective due to reduced fluid control in the smaller tooth dimensions. Also, structural integrity is lost when the tooth width is reduced, making each tooth more easily deformable during manufacture and when in contact with sample reservoirs and the substrate.
Simply making the teeth smaller to accommodate more samples non-reproducibly reduces the amount of sample per tooth deposited/transferred, lowering the ability to detect target components of the sample after they have been separated. Additionally, variable sample deposition with increasing the number of teeth per applicator comb can cause lane contamination so that adjacent lane samples bleed into one another rendering the samples as unreliable for measurement.
In previous efforts to generate a greater sample density on the gel, the teeth were manufactured to be narrower. However, a direct reduction in size/geometry led to inconsistent liquid management and generally reduced liquid deposition. The volume of the liquid to be applied must be of sufficient volume to accommodate the sensitivity of the assay. The narrower tooth must therefore have the ability to both load appropriate volumes and unload those volumes in a controlled and reproducible fashion. A narrower tooth without additional surface to adsorb the liquid will result in the liquid droplet surface protruding too far from the surface of the tooth, increasing the necessary surface tension to hold the liquid droplet in place. The flash dimension of each tooth is insufficient to maintain surface tension of the liquid droplet to prevent premature liquid release if the tooth is too narrow and no other provision is made to hold the liquid.
The present invention is directed to overcoming these and other deficiencies in the art.